525 Golden Gate Avenue, 13th Floor San Francisco San Francisco, CA 94102 T 415.554.3155 Water Sewer F 415.554.3161 Operator of the Hetch Hetehy Regional Water System TTY 415.554.3488 January 8, 2014 TO: Commissioner Vince Courtney, President Commissioner Ann Moller Caen, Vice President Commissioner Francesca Vietor Commissioner Anson Moran Commissioner Art Torres THROUGH: Harlan L. Kelly, Jr., General Manager FROM: Steven R. Ritchie, Assistant General Manager, Water RE: The Rim Fire - Hetch Hetehy Watershed Effects Report The Rim Fire - Hetch Hetehy Watershed Effects Report was prepared in response to widespread concerns about impacts to Hetch Hetehy Reservoir water quality following the 2013 Rim Fire. An interdisciplinary team of SFPUC scientists, water system operators, and planners from the Hetch Hetehy Water and Power, Water Quality, and Natural Resources and Lands Management Divisions of the Water Enterprise completed this comprehensive study following field observations during and after the Rim Fire incident. This report is a summary of those scientific efforts, and provides a detailed overview of Rim Fire impacts, both current and anticipated, as well as a comparative study of other fires within the Hetch Hetehy watershed. Though the 2013 Rim Fire was a significant wildland fire, the 3 r d largest in California, ultimately, its impacts within the Hetch Hetehy watershed are expected to be negligible with no impact to water quality. Only 1.8% of the watershed draining to Hetch Hetehy Reservoir fell within the Rim Fire perimeter. Of that acreage within in the fire perimeter, only 8% received Edwin M. Lee moderate to high soil burn severity and 23% received low burn severity. Field Mayor evidence indicates that though there is some increase in erosional processes Vince Courtney associated with fire affected soil conditions, the net increase in watershed President erosion is negligible. The historical record of water quality for the watershed Ann Moller Caen Vice President also supports negligible expected impact to water quality. Francesca Vietor Commissioner Though the Rim Fire has had, and will continue to have, impacts on the Hetch Anson Moran Hetehy watershed, the Hetch Hetehy Regional Water System retains the ability Commissioner deliver high quality drinking water to its wholesale and retail customers. This Art Torres Commissioner report will now add to the historical record and assist us in continuing to Harlan L. Kelly, Jr. monitor the impacts of wildland fires on watershed lands. General Manager Attachment Sen/ices ofthe San Francisco Public Utilities Commission Rim Fire – Hetch Hetchy Watershed Effects Photo taken September 26, 2013 Prepared by: Adam Mazurkiewicz – Hetch Hetchy Water and Power Chris Graham – Hetch Hetchy Water and Power Rebecca Leonardson – Hydrology and Water Systems Modeling Robert Clark – Water Quality Division Table of Contents 1 Executive Summary .............................................................................................. 1 2 Introduction ..........................................................................................................2 2.1 Post Fire Response .........................................................................................3 3 Field Observations ................................................................................................4 3.1 Rim Fire within the Hetch Hetchy Watershed.............................................4 3.2 Fire Observations ...........................................................................................5 3.3 Post Rain Event Observations .......................................................................7 3.4 Hydrologic Field Measurements .................................................................. 8 3.5 Water Quality Monitoring ...........................................................................10 3.5.1 SCADA System.......................................................................................10 3.5.2 Routine Sampling.................................................................................. 11 3.5.3 Supplemental Monitoring.....................................................................12 4 Sediment/Erosion Modeling.............................................................................. 17 4.1 Sediment Delivery Rates.............................................................................. 17 4.2 ERMiT Modeling .......................................................................................... 17 5 Hetch Hetchy Watershed and Fire History ......................................................18 6 Historical Water Quality ....................................................................................21 7 Summary and Conclusions................................................................................ 23 8 Acknowledgements............................................................................................ 24 9 Appendices ..........................................................................................................25 1 Executive Summary The Rim Fire is the 3rd largest wildland fire in California’s history at 257,314 acres and the largest in Yosemite National Park’s history. Wildland fires are a natural part of the Sierra Nevada landscape and occur nearly every year within the Hetch Hetchy drainage. Approximately 5,080 (7.93 sq. mi) acres of the Hetch Hetchy watershed, or approximately 2% of the Hetch Hetchy drainage, falls within the Rim Fire perimeter. A majority of the affected watershed has been classified with a burn severity of low to no burn. An evaluation by the National Park Service Burn Area Emergency Response team indicates that there will be no significant impacts to water quality and quantity at Hetch Hetchy Reservoir due to the relatively small area within the watershed affected by the fire. A group of field 1 experts from the SFPUC reviewed historic fire patterns and further evaluated the fire effects, reservoir water quality conditions, and potential increases in erosion due to the Rim Fire. The area within the Hetch Hetchy watershed affected by the Rim Fire falls within the magnitude and footprint of historical fires conditions. Limnological and water chemistry monitoring during the fire found no effect on water quality conditions. Field surveys of soil conditions indicate a decrease in infiltration rates and an increase in hydrophobicity, however the measured conditions fall within the typical range for local soil types. An increase in erosional processes associated with fire affected soil conditions was found, however due to the limited area affected the net increase in watershed erosion is negligible. There are few historical events of impaired water quality at Hetch Hetchy and they are associated with major storm events and have no correlation to changes in the landscape. The study results indicate that the effects of the Rim Fire are expected to be negligible and there will be no impact on water quality. 2 Introduction On August 17, 2013 an escaped campfire ignited what became known as the Rim Fire. The fire started in the Clavey River drainage along Jawbone Ridge, approximately 2.5 miles upstream of the confluence of the Tuolumne River. The fire perimeter ultimately encompassed 257,314 acres (402 sq. mi) including areas within the Hetch Hetchy, Cherry and Eleanor watersheds (Figure 1.). The Rim Fire is the third-largest in California history and is nearly equivalent in size to the Hetch Hetchy watershed. The fire expanded greatly in size between August 21st and August 30th – from 16,204 acres to 201,795 acres. Within this time period the fire doubled in size on August 22nd (53,829 to 105,622 acres). The rapid expansion was due to remote, steep terrain, extremely dry fuels, and windy conditions which led to difficult firefighting conditions. Expansion of the fire slowed as it met the fire retardant barriers and large fire breaks on the north and south flanks. Progression eastward (in the vicinity of Hetch Hetchy, Cherry Reservoir and Lake Eleanor) also slowed as the fire encroached on areas with lower canopy densities, less available fuels and increased exposed granite bedrock. The fire lines began to hold the north and south flanks near August 31st, while a majority of the east flank was allowed to reach natural granite fire breaks. Weather conditions in mid-September and a rain event on September 21st slowed the growth of the fire towards the natural eastside fire breaks which led to continual postponement of the forecasted containment date. The fire was considered contained on October 24th and as of October 25th over $127 million was spent on firefighting costs. 2 2.1 Post Fire Response The U.S. Forest Service (USFS) and the National Park Service (NPS) convened a Burn Area Emergency Response (BAER) Team to assess post-fire conditions and address emergency stabilization issues prior to the onset of the winter season (see Appendix 1). Due to differences in land management objectives, a BAER team was established for each agency. The two teams worked together performing field and modeling evaluations but developed their own recommendations for each of their administration areas and specific values at risk. The USFS team produced a series of Specialist Reports (Appendix 1a-1h) which identify values at risk due to fire related impacts. The focus of BAER recommendations are on protection of life and property, including roads, buildings, water quality, trails, campgrounds, and private properties.